Qt Generic Drag and Drop event filter

dragdropfilter.cpp

#include <QDragEnterEvent>
#include "dragdropfilter.h"

bool DragDropFilter::eventFilter(QObject* obj, QEvent* event)
{
	auto w = qobject_cast<QWidget*>(obj);
	if(w == nullptr) {
		return true;
	}

	QString highlightColor = w->palette().color(QPalette::Highlight).name(QColor::HexRgb);
	QString selectedSS = QString{"background-color:%1;"}.arg(highlightColor);

	switch (event->type()) {
	case QEvent::DragEnter:
	{
		w->setStyleSheet(selectedSS);
		auto dragEnterEvent = static_cast<QDragEnterEvent*>(event);
		dragEnterEvent->acceptProposedAction();
		emit dragEntered(dragEnterEvent->mimeData());
		break;
	}
	case QEvent::DragMove:
	{
		auto dragMoveEvent = static_cast<QDragMoveEvent*>(event);
		dragMoveEvent->acceptProposedAction();
		break;
	}
	case QEvent::DragLeave:
	{
		w->setStyleSheet("");
		auto dragLeaveEvent = static_cast<QDragLeaveEvent*>(event);
		dragLeaveEvent->accept();
		emit dragDeparted();
		break;
	}
	case QEvent::Drop:
	{
		w->setStyleSheet("");
		auto dropEvent = static_cast<QDropEvent*>(event);
		dropEvent->acceptProposedAction();
		emit dragDropped(dropEvent->mimeData());
		break;
	}
	default:
		return QObject::eventFilter(obj, event);
	}

	return true;
}

dragdropfilter.h

#include <QObject>
#include <QMimeData>

class DragDropFilter : public QObject
{
	Q_OBJECT
protected:
	bool eventFilter(QObject *obj, QEvent *event) override;
signals:
	void dragEntered(const QMimeData* mimeData);
	void dragDropped(const QMimeData* mimeData);
	void dragDeparted();
};

usage:
auto dragDropHandler = new DragDropFilter;
someWidget->installEventFilter(dragDropHandler);
someWidget->setAcceptDrops(true);

// connect signals & slots
connect(dragDropHandler, &DragDropFilter::dragDropped, this, [this](const QMimeData* mimeData){}); // etc